Semiconductor power devices are specialized devices that are used as switches or rectifiers in power electronics circuits. They are characterized by their ability to withstand high voltages and large currents as well as the high temperatures associated with high power. As such, certain problems faced by standard transistors when they are operated in high voltage conditions are of particular concern in the realm of power transistors. In addition, the conditions under which a transistor breaks due to the application of large voltages or currents must be carefully scrutinized when designing a power device.
Device breakdown is a term used to describe various issues faced by devices when a certain point is reached at which their performance alters in a nonlinear fashion. One example of device breakdown is the “kink effect” which results from an increase in the body potential of a field effect transistor. However, breakdown is not a phenomenon that is limited to field effect transistors as there are known breakdown modes for nearly all semiconductor devices including bipolar junction transistors, diodes, resistors, capacitors, and generally all transistor and rectifier devices.
The kink effect can be explained with reference to FIG. 1 which includes a cross section 100 of a semiconductor device. The field effect transistor in cross section 100 provides a conductive path between source region 101 and drain region 102 in response to a voltage applied to the device via an isolated gate electrode in gate stack 103. The conductive path is formed through body region 104. The conductive path includes a channel through body region 104. A schematic of this field effect transistor 105 has been drawn over cross section 100 to illustrate its operation relative to the cross section. The conductivity types of source and drain regions 101, 102 are the opposite of the conductivity type of body region 104. As a result, cross section 100 can also represent a parasitic BJT where body region 104 serves as the base of the BJT. A schematic of this parasitic BJT 106 has been drawn over cross section 100 to illustrate its operation relative to the cross section. The kink effect occurs when the parasitic BJT is activated by a build-up of charge in body region 104 caused by charge carriers associated with field effect transistor 105 as it is operated in a high power regime. Although device breakdown is sometimes used intentionally as part of a design, it is more often a point of operation that designs are meant to avoid.